This application is the national phase under 35 U.S.C. xc2xa7 371 of PCT International Application No. PCT/JP00/07085 which has an International filing date of Oct. 12, 2000, which designated the United States of America.
The present invention relates to a high frequency amplifying device for use in a satellite communication, ground microwave communication, mobile communication, and the like.
Generally, a high frequency amplifier using an NPN bipolar transistor of the BJT, HBT, or the like takes on a constant voltage biasing circuit that applies a constant voltage to the base in order to achieve a high power output and high efficiency. When a constant bias current is applied to the base, and when power of a high frequency input signal increases and generates a rectified current, the base voltage drops in order to maintain the constant current. Accordingly, when the power of input signal increases, since the amplifier operation rapidly approaches to the B-class, the saturation power decreases, and the high power output and high efficiency cannot be achieved. When a constant bias voltage is applied to the base, on the other hand, since the base voltage will not drop, the biasing class does not change, and a greater saturation power output and higher efficiency can be attained in comparison to the case of the constant current biasing. Therefore, a constant voltage biasing circuit that does not lower the base voltage, becomes necessary even when there is an increase of the base current with an increase of the power of input signal.
FIG. 1 is a circuit diagram illustrating a high frequency amplifying device, in that a base current compensating current mirror circuit is used for the constant voltage biasing circuit, which is presented, for example, in xe2x80x9cIntroduction To Functional Circuit Design of Analog ICs, IC Designing Method Using Circuit Simulator SPICExe2x80x9d (written by Hidehiko Aoki, issued by the CQ publisher, Sep. 20, 1992, page 74).
In the drawing, reference numeral 1 signifies a high frequency amplifier using an NPN bipolar transistor such as the BJT, HBT, or the like, as the amplifying element, and 2 signifies a constant voltage biasing circuit that supplies a base bias voltage to the high frequency amplifier 1.
In the high frequency amplifier 1, reference numeral 3 signifies an NPN bipolar transistor such as the BJT, HBT, or the like, 4 signifies the ground connected to the emitter terminal of the NPN bipolar transistor 3, 5 signifies a high frequency signal in,put terminal, 6 signifies a high frequency signal output terminal, 7 signifies a base bias terminal, 8 signifies a collector bias terminal.
In the constant voltage biasing circuit 2, reference numeral 11 signifies an NPN bipolar transistor such as the BJT, HBT, or the like, which configures a current mirror circuit together with the NPN bipolar transistor 3 of the high frequency amplifier 1, whose base terminal is connected to the base bias terminal 7, whose emitter terminal is connected to the ground 4. Reference numeral 12 signifies an NPN bipolar transistor such as the BJT, HBT, or the like, for a base current compensation, whose base terminal is connected to the collector terminal of the NPN bipolar transistor 11, whose emitter terminal is connected to the base terminal of the NPN bipolar transistor 11. Reference numeral 13 signifies a resistor connected between the collector terminal of the NPN bipolar transistor 12 and a power supply/voltage setting terminal 15, and 14 signifies a resistor connected between the base terminal of the NPN bipolar transistor 12 and the power supply/voltage setting terminal 15.
Next, the operation will be described.
A high frequency signal Pin is input to the high frequency amplifier 1 through the high frequency signal input terminal 5, and is output from the high frequency signal output terminal 6, after being amplified by the high frequency amplifier 1. A base voltage Vb and a base current Ibrf to the high frequency amplifier 1 are supplied from the constant voltage biasing circuit 2, and a collector current Icrf and a collector voltage Vc to the high frequency amplifier 1 are supplied from the collector bias terminal 8.
In the constant voltage biasing circuit 2, the base voltage Vb and the base current Ibrf are determined as follows. Here, it is supposed that a size of the NPN bipolar transistor 11 that forms the current mirror together with the high frequency amplifier, 1 is 1, a size of the NPN bipolar transistor 3 of the high frequency amplifier 1 is N, and a size of the NPN bipolar transistor 12 for the base current compensation is M. Also, it is supposed that these three NPN bipolar transistors 3, 11, 12 have the same structure and the same current amplification factor xcex2. Further, the contact voltage Vref, the currents Iref, Icdc1, Ibdc1, Icdc2, Iedc2, Ibdc2, Ibrf, Icrf, and the resistor Rref are defined as shown in FIG. 1.
When a power supply voltage Vpc is supplied from the power supply/voltage setting terminal 15 of the constant voltage biasing circuit 2, the reference current Iref of the current mirror is given by the following expression.
Iref=(Vpcxe2x88x922*Vb)/Rref
With regard to this reference current Iref, the collector current Icrf of the NPN bipolar transistor 3 of the high frequency amplifier 1 is given as follows.   Icrf  =            N              1        +                              1            +            N                                β            ·                          (                              1                +                β                            )                                            ⁢    Iref  
Where the base bias voltage Vb of the NPN bipolar transistor 3 of the high frequency amplifier 1 is set as follows.
Vb=(Vpcxe2x88x92Iref*Rref)/2
The base current Ibrf flowing in this case becomes as follows.
Ibrf=Icrf/xcex2
In this manner, the constant voltage biasing circuit 2 supplies the base voltage Vb and the base current Ib as the output thereof.
Since the conventional high frequency amplifying device is configured as above, when the high frequency input signal Pin increases and generates a base rectified current xcex94Ib, the base voltage Vb lowers by a voltage drop of xcex94Vb. Therefore, when the high frequency input signal Pin increases, the biasing class of the high frequency amplifier 1 approaches to the B-class, and the saturation output power and efficiency are decreased, which is a problem. Hereunder, the operation to cause the voltage drop xcex94Vb will be explained.
In the conventional technique, a case will be examined, in which the input power of the high frequency amplifier 1 increases and generates the base rectified current of xcex94Ib, and consequently the constant voltage biasing circuit 2 increases the output of the base current Ibrf by xcex94Ib. When the base current Ibrf increases by xcex94Ib, assuming that the emitter current Iedc2 of the NPN bipolar transistor 12 for the base current compensation increases by xcex94Iedc2, and the base current Ibdc1 of the NPN bipolar transistor 11 that forms the current mirror decreases by xcex94Ibdc1, there is the following relation on the variations of these currents.
xcex94Ib=xcex94Iedc2+xcex94Ibdc1
Next, a variation xcex94Icdc1 of the base current Icdc1 of the NPN bipolar transistor 11 that forms the current mirror is given as follows.
xcex94Icdc1=xe2x88x92xcex2*xcex94Ibdc1
Here, assuming that the reference current Iref is almost constant, a variation xcex94Ibdc2 of the base current Ibdc2 of the NPN bipolar transistor 12 for the base current compensation is given as follows.
xcex94Ibdc2=xe2x88x92xcex94Icdc1=xcex2*xcex94Ibdc1
Therefore, the variation xcex94Iedc2 of the emitter current Iedc2 of the NPN bipolar transistor 12 for the base current compensation is given as follows.
xcex94Iedc2=(1+xcex2)*xcex94Ibdc2=xcex2*(1+xcex2)*xcex94Ibdc1
Therefore,
xcex94Ib=xcex94Iedc2+xcex94Ibdc1=xcex94Ibdc1*{1+xcex2*(1+xcex2)}=xcex94Ibdc1*(1+xcex2+xcex22)
Therefore, xcex94Ibdc1 is given as follows.       Δ    ⁢          xe2x80x83        ⁢    Ibdc1    =            Δ      ⁢              xe2x80x83            ⁢      Ib              1      +      β      +              β        2            
The voltage drop at this moment of the NPN bipolar transistor 11 that forms the current mirror, namely the voltage drop xcex94Vb of the output voltage Vb is given as follows.       Δ    ⁢          xe2x80x83        ⁢    Vb    =                    q        nkT            ⁢              ln        (                  1          -                                    Δ              ⁢                              xe2x80x83                            ⁢              Ib                                      Is              ·                              (                                  1                  +                  β                  +                                      β                    2                                                  )                            ·                              e                                  qVb                  nkT                                                                    )               less than     0  
Where n is the compensation coefficient, k is the Boltzmann""s constant, T is the absolute temperature, q the electric charge, and Is the saturation current.
Accordingly, in the high frequency amplifier of the conventional technique, when the high frequency input signal Pin increases and generates the base rectified current xcex94Ib, the base voltage Vb generates the voltage drop of xcex94Vb; and as a result, the biasing class of the high frequency amplifier 1 approaches the B-class when the high frequency input signal Pin increases, which leads to a problem that the saturation output power and the efficiency are decreased.
The present invention has been made in order to solve the foregoing problem, and an object of the present invention is to achieve a high frequency amplifier that maintains a high efficiency, even if the high frequency input signal increases and generates the base rectified current.
The high frequency amplifying device according to this invention is provided, between a first and second resistors and a third NPN bipolar transistor, with a first and second PNP bipolar transistors forming a current mirror that uses a collector current of the third NPN bipolar transistor as a reference current, and determines a collector current of a second NPN bipolar transistor.
With this configuration, designing a size ratio of the first and second PNP bipolar transistors forming the current mirror so as to approximate a voltage drop to just zero, or a value infinitely close to zero will suppress the voltage drop of the base voltage, when the high frequency input signal increases and generates a base rectified current, which effects a high power output and high efficiency.
Further, varying the size ratio of the first and second PNP bipolar transistors forming the current mirror will adjust, i.e., increase, regularize, or decrease the base voltage, when the high frequency in put signal increases and generates the base rectified current, thus effecting a function to adjust the base voltage.
The high frequency amplifying device according to this invention is provided, between a first and second resistors and a third NPN bipolar transistor, with a first and second PMOS transistors forming a current mirror that uses a collector current of the third NPN bipolar transistor as a reference current, and determines a collector current of a second NPN bipolar transistor.
With this configuration, designing a size ratio of the first and second PMOS transistors forming the current mirror so as to approximate a voltage drop to just zero, or a value infinitely close to zero will suppress the voltage drop of the base voltage, when the high frequency input signal increases and generates a bases rectified current, which effects a high power output and high efficiency.
Further, varying the size ratio of the first and second PMOS transistors forming the current mirror will adjust, i.e., increase, regularize, or decrease the base voltage, when the high frequency input signal increases and generates the base rectified current, thus effecting a function to adjust the base voltage.